Variable pitch propeller



Aug. 5, 1947. v H. MURPHY EI'AL 2,425,261

VARIABLE PITCH PROPELLER Filed Dec. 9, 1943 3 Shouts-Shoot i floward C(17) ATTORNE Aug. 5, 1947. H. MURPHY EI'AL. 2,425,261

VARIABLE PITCH PROPELLER Filed Dec. 9, 1945 3 Sheets-Sheet 2 ATTORNEY Aug. 5, 1947. MURPHY ETAL- I 2,425,261

- VARIABLE PITCH PROPELLEB Filed Dec. 9, 1945 s Sheets-Sheet s ATTORNEY Patented Au 5, 1947 I 2,425,261

UNITED STATES" PATENT, OFFICE Howard Murphy, Glen Ridge, and Robert E.

Linse, Troy Hills, N. J., assignors to Cur-tiss- Wright Corporation, a corporation of Delaware Application December 9, 1943, SerialNo. 513,582

3 Claims. (Cl. 170-463) 1 v This invention relates primarily to propellers and more particularly to hydraulically actuated propeller blade pitch changing mechanisms.

Heretofore, most pitch changing mechanisms of the above description have been so constructed 5 tuated pitch changing mechanism for variablethat the hydraulic unit is necessarily located on pitch propellers which is of extreme simplicity, the opposite side of the propeller from the engine positive and dependable in operation, light in that drives it. This is'objectionable because no weight, and which may be easily and cheaply satisfactory method has yet been devised for manufactured, assembled and maintained. efiectively venting and draining hydraulic units Another object of the present invention is to thus located. Such constructions are also undeprovide a propeller of the above type wherein no sirable because of the resulting weight concensprings or counterweights are employed in any tration at a point so remote from the propeller partof the mechanism, and in which all hydraulic shaft bearings, which are generally mounted in connections thereto are outside of the engine the engine housing. As a consequence, unwarcasing. ren ly hi h vibrat ry and bending stresses are Another object of the invention is to provide a frequently attributable to arrangements of this hydraulically actuated propeller blade pitch typ In O der t e co e th 0 J'eC changing mechanism comprising an annular cyli n h ve be n propo ed wh the hydraulic inder and longitudinally movable piston therein, mechanism is located between the propeller and concentrically mountedwlth the propeller shaft engine, but while that location. is desirable, the and rotatable therewith. designs in question include faults that render Another object of the invention is to provide a them unsatisfactory in actice as is apparent propeller of the above description wherein the from What followscylinder and piston are located between the en- There are two classes of the last-mentioned degum and propeller so as to concentmfie the weight class the use of I hydraulic thereof close to the bearings that support the promotor with impeller vanes constitutes the prinpener shaft and so as to permit of the use of (pal feature and it is ll that the cost proved means for supplying hydraulic fluid to the of manufacturing and maintaining such mechcylinder anisms is extremely high. In addition, they are heavy, bulky and subject to excessive leakage. In the other class, the hydraulic unit consists essentially of a stationary cylinderand non-rotating piston. This construction is obviously objectionable because of the fact that the total force ex-,

erted by the piston must be transmitted to the blade turning mechanism, located on the propeller hub, through the medium of a thrust bearing running at the same high speed as the propeller.

To those familiar with theart, a bearing which would meet such severe operating conditions is enumerated in the preceding paragraphs, and

which is so compact that it can readily bein- 2 stalled in small space between any propeller and the engine that drives it. i I Another object of the present invention is to provide an improved and novel hydraulically ac- Another object of the invention is to provide a hydraulically actuated pitch changing mechanism for variable pitch propellers, which does not require any drilling or cutting of any part of the propeller shaft, and inwhich no fluid is carried in the interior thereof. Such a design is advant'ageous in that it does not weaken the propeller shaft and leaves the usually hollow central portion thereof entirely free for gun-fire, etc. I

Another object of the invention is to provide.

an improved and simplified hydraulic device for transferring fluid under pressure from one mem trically with a rotatable shaft wherein no fluid sesi between the ring and the shaft is required,

and in which the fluid seal surfaces are flat.

A further object of the invention in connection with the above is to provide a fluid transfer arrangement which is readily accessible and which may be easily adjusted to compensate for wear, if necessary.

A further object of the invention in connection.

with the above is to provide an improved device for conveying fluid between relatively moving members wherein said members are hydrostatically balanced with respect tonne-another.

A still further object of the invention is to provide a system for lubricating the propeller blade thrust bearings, and other moving parts mounted on or in the propellerhub wherein the lubricant is completely isolated and independent of the fluid in the hydraulic system employed to vary the pitch of the propeller blades.

Another object of the invention is to provide means for venting and draining the hydraulic pitch changing cylinder by centrifugal action in such a manner that any fluid, such as oil, leaking into the vented part of the cylinder is 'returned to the engine oil sump or other source of supply utilized in the hydraulic system.

Another object of the invention is to provide means for'continnously equalizing during rotation of the propeller hub the amount oflubricant carried in all blade sockets, regardless of inequalities in the original distribution thereof and regardless of leakage thereof from any one or more of the sockets.

These and other objects and advantages'of the invention will be made more apparent herein after by the following detailed description when taken in conjunction with the accompanying drawings, which illustrate one embodiment of the invention.

In the drawings,

Fig. 1 is a sectional view of a propeller blade pitch changing mechanism constructed in accordance with the principles of the present invention, with the section above the longitudinal center line taken in a plane parallel to and through the axis of the propeller shaft and the axis of one of the blade sockets; the lower half of the section being ina plane parallel to and partially through the propeller shaft axis but perpendicular to the axis of another blade socket spaced 120 from the one above;

Fig. 2 is a front end view partly in section the propeller hub of Fig. 1;

Fig. 3 is a horizontal sectional view taken substantially on line 3-3 of Fig. 2;

Fig. 4 is an enlarged detail view of a part of the oil leakage collecting and draining elements:

Fig. 5 is a vertical sectional view taken substantially on line 5-5 of Fig. 1;

Fig. 6 is a vertical sectional view taken substantially on line 6-5 of Fig. 1; and

Fig. '1 is an enlarged detail view partly in section taken on line 1-1 of Fig. 1.

Referring flist'to Figs. 1 and 2, a propeller hub, indicated generally by reference numeral II, is shown mounted on a propeller shaft II, which is supported and driven 'by an engine having a nose housing indicated by the reference numeral Ill.

' The propeller shaft i2 is adapted to drive the propeller hub ll through the usual means, such as interengaging splines 13.. In the illustrated embodiment of the present invention, as most clearly shown in Fig. 2, the propeller hub H has three blade sockets, each indicated generally by reference numerals II. It is to be understood,

when? r however, that no limitation is impoud in this connectionpfor obviously either a greater or smaller. number of blades could be used without affecting anyof the principles involved. The 5 'blade sockets. it support associated propeller blades, only the shanks 38 of which are shown, in such a manner, a hereinafter described in detail, that the pitch thereof may be altered.

Secured to the front of the propeller hub or the left hand end, as shown in Fig. 1, by screws such as ii is a cap li which serves to keep foreign material, such as dust and dirt, out of the propeller shaft and hub mounting units. The propeller hub II has on its right hand end, as shown min Fig. 1, a radially extending circular flange 11 formed integrally with the blade sockets I4, and secured to the right hand or engine side of this flange, bybolts such as It, is a cylinder l8, concentrically mounted with the propeller shaft I2. Secured to the right hand end of the cylinder I! by the bolts l-S and cap screws, such as "-0, Fig. 6,'is a circular head or cover member 2|,

Fig. 1, having a central bore adapted to fit slidably on the propeller shaft l2. The cylinder ll together with the propeller shaft l2 and head 2! form an annular hydraulic pressure chamber which is closed at the propeller end by the hub II and flange l1. Inasmuch as the cylinder 18 and the head 21 are secured to the propeller hub ll, they rotate therewith and with the propeller shaft 12. In the central bore of the head 21 is a groove 22 in which a packing ring 22-a of suitable material may be provided to prevent the escape of oil from the hydraulic chamber along the shaft [2.

Located in the above described hydraulic chamher is an annular piston 22 which is adapted to move longitudinally therein so as to effect pitch changes of the propeller blades in a manner hereinafter explained. The piston 23 has secured to the right hand face thereof by cap screws, such as 24, and a metal disc, such as 26, a double flanged packing ring 25 of suitable material, such as leather, which engages both the inner wall of the cylinder is and the outer surface of the propeller shaft l2 to prevent the escape of hydraulic fluid past the piston 22. The outer flange of the packing ring 25 is held against the cylinder 18 by centrifugal force and its inher flange is pressed against the propeller shaft by a circular spring 26-11. Secured to the piston 23 are three rack rods 21, one for each propeller blade, which are cylindrical in cross-section throughout the end portions thereof. .Each of the rods 21 is slidably mounted in a bore 28. parallel with the propeller shaft, formed in the body of the hub H. The outer or left end of each bore 28, as viewed in Fig. 1, is closed by a plug 29, and the space at the end of the bore 28, between the rod 21 and the plug 28, is vented by a groove 29--a formed in the rod 21. The rods 21 are secured to the piston 23 by nuts, such as 30, in threaded engagement therewith and are prevented from rotating in their mountmg holes in the piston by keys, such as 3|, Fig, 3. The rack rods 21 serve to support and guide the piston 23 in its back and forth movement in the cylinder 18, and, in the preferred embodiment, a slight amount of clearance is provided between the piston and cylinder and between the central bore in the piston and the shaft 12, so.

that only the hydraulic packing ring 25 bears on the cylinder wall and on the shaft. Packing rings such as 32 in the flange portion '11 .ofithe 15 hub surround the rack rods 21 to prevent leakage to and from the hydraulic chamber and the w blade sockets.

In the central portion-of each rack rod 21,

Fig. 1, 2 and 3, a rack of gear teeth 33 is formed,

and these teeth are adapted to engage cooperating teeth 35 of a spur gear segment 34-a formed on a split sleeve member 34, which is split,along the longitudinal axis thereof and. is clamped to an associated blade shank 36 by a clamping ring 31 of conventional design. All of the spur gear.

segments 34 a secured to the "several blade shanks 36 have the same pitch diameter. The blade shank 36 is shown in full in Fig. 1 and has radial flanges or' shoulders, such as 38 and 39, engaging mating flanges 4| and 42, respectively, on the inside of the split sleeve 34." In

lowermost of a stack of ball thrust bearings- 46.'

The outer races 41 of the bearings 46 engage the inside of the blade socket,|4 and are held therein by a nut 48 in threaded engagement therewith. A locking key 49 is provided to prevent rotation of the nut 48 relatively to the blade socket after beingtighteried, and the key. is held in place by screws, such as 5|.

More than one key 49 may be employed, such keys being placed in radial "slots in the upper surfaces of the blade socket |4' and thelocking nut 48. A packing ring 52 surrounds the blade sleeve 34 at the nut .46 to prevent leakage of lubricant from the blade socket. I

The inner end of the blade shank 36 is recessed and has therein a thrust member 53 faced with a non-metallic disc 54 which bears on a mating surface such as 56 formed on the longitudinal portion of the hub The radial force developed by the tightening of thelocklng nut 48 is transmitted through the thrust bearing 46,

sleeve 34, blade shank 36, thrust member '53 and disc 5.4 to the surface 56 of the propeller hub, and thus serves as means whereby the thrust bearing 46 may be preloaded.

The head 2| of the hydraulic cylinder l8 has, as shown in Fig. 1, an extension or sleeve portion 51 surrounding the propeller shaft |2. The extreme end of the sleeve portion 51 is threaded to engage a nut 58, and has a smooth cylindrical surface to the left of said threaded end upon which is located an oil, or other fluid, transfer ring 59. The oil transfer ring 59 fits slidably upon the sleeve portion 51 of the head 2|, and

head 2| has a radial surface 6|, that is ground flat, against which the left hand face of the oil transfer ring abuts. The inside face 58a of the nut 58, against which the right hand face of the transfer ring abuts, is also ground flat.

The oil transfer ring 59 has a relatively deep circular groove 62 in its left hand face and a relatively shallow circular groove 61 in its opposite face. It is preferable, for reasons that will later be made apparent, that these two grooves 62 and 61 be concentric and have the same inside and outside diameters, though obviously such a construction is not essential to satisfactory operation of the oil transfer ring. A hole 63 is drilled straight through the ring 59 to connect the grooves 62 and 61 with each other. A radial hole 64 is drilled from the outside periphery of the ringja to meet the hole '63, and is tapped or otherwise adapted to take a fitting 64 to which may be connected a tube 66, preferably .of the armored flexible type, leading to an oil pump or OthGlYSOllIfC of fluid pressure supply, by way of suitable manual or automatic control valves, or ahydesirable combination of such valves.

" One or more holes or passageways such as 68 are drilled through the head 2| opposite the groove 62in the oil transfer ring 59 whereby an 'oil connection is established from the transfer ring 59 to that section; of the hydraulic chamher to the right of the piston 23. Accordingly,

oilentering the ring 59 under pressure from the tube 66 may pass to the cylinder to force the piston to the left.

In order to prevent the oil transfer ring 59 from rotating with the propeller shaft and hub assembly, a pin 69 is forced radially into a suitable hole in the transfer ring and has its opposite end retained in a longitudinal slot 69a in the interior of a stationary oil collector casing 1|, hereinafter described. In accordance with the above-described arrangement the transfer of oil 7 or other fluid under pressure is effected between a non-rotating element (the oil transfer ring 59) and a rotating element (the head 2 I) leakage being prevented wholly by sealing contact between the flat surfaces thereof. These flat surfaces are much easier to machine,-to make oil tight and to maintain than circular surfaces such as are used in prior art arrangements, and in addition the arrangement described provides means whereby the 01] seal surfaces may be readily adjusted relatively to each other at assembly and in service without opening or disturbing the engine housing, thus providing means for quickly compensating for wear, should any occur. Obviously, such adjustments may be made-by moving the nut 58 along the threaded portion of the sleeve 51. The

- nut 58 is locked in place by a screw such as 12,

- the two radial faces thereof are ground flat. The

Figs. 1 and 7. By means of slightly oversize drilled holes such as 13 extending radially through the nut 58 and differently spaced tapped h'oles such as 14 in the sleeve 51 for the screw 12, the nut may be adjusted longitudinally of the sleeve portion 51 in extremely small increments. The screw 12 has a hole 10 drilled through its shank close to its head, and when the screw is in place a locking wire is passed through the hole 10; the locking wire also being passed through a suitable circular groove 15 cutin theouter periphery of the nut 58.

In addition to the several advantages already described that are possed by the type of fluid transfer device included in this invention, there is the important feature of a completely balanced construction, whereby the pressure of the fluid has no influence nor effect tending to force I ring 59 each have the same area facing the-two moving contact-surfaces 6| and 58-11 on the head 2| and nut 58 respectively. Consequently, when fluid under pressure enters the ring 59 through the tube 66, the total pressure exerted thereby against the'surface 6| is equal and-opposite to the total pressure exerted against the surface 58-11, and, therefore, the ring 59 is completely balanced longitudinally and the fluid-seal surfaces thereof are not forced against either 'of ,7 the contacting surfaces 8| or 58-0 by the action of the fluid.

The oil collector casing 1| is, in the manner hereinafter described, adapted to collect oil that may leak or be elected from the hydraulic cham- 5 her or from the oil transfer ring 88. The casing 1| which is split, preferably in a horizontal plane, to facilitate installation, is secured to a plate 18 by bolts such as 11, and carries a packing ring 18 surrounding the cylinder portion ll of the n hydraulic chamber. The two halves of the casing 1| are bolted together by means of bolts 18, and the plate 18 is secured to the outer end, or nose ll, of the engine by any suitable means, such as studs or tap bolts, not shown.

1 The oil collector casing 11 surrounds the oil against the inside surface thereof and convey the,

same to the lower half of the casing. The oil pressure supply tube 88 extends through the oil collector casing 1i where the two halves join, and preferably has a gasket 84 surrounding the same as shown in Fig. l to form an oil seal and deaden vibrations.

The left hand end of the hydraulic cylinder 18 or the part thereof to the left of the piston 28 as shown in Fig. l is vented by means of a passageway in the form of a hole 86 which leads from this part of the chamber through the cylinder wall and head M to the chamber formed by the oil collector casing 1i, the engine nose plate 16 and the head 2!. Accordingly, any oil leaking past the piston 23 and any lubricant leaking past 40 the rods 21 from the hub into the left hand end of the cylinder chamber will be thrown by centrifugal force into the passageway 86 and through it into the oil collector casing 1i, whence it will,

be conveyed by gravity through the connection 82,

Fig. 4, to the engine oil sump or other source of fluid supply which is ordinarily maintained at approximately atmospheric pressure.

Each blade socket ll on the hub carries lubricant for lubricating the thrust bearings 46 and 5 for the movable parts of the pitch changing mechanism located therein, such as the spur gear segment 84-41 and the rack rod 38. If the lubricant is not equally distributed among all of the blade sockets, an objectionable unbalanced condition of the propeller may result, and some of the bearings and other parts may be insufflciently lubricated. Consequently, in accordance with another feature of the invention, means are provided whereby the total lubricant in all of the blade sockets'is equally distributed through the action of centrifugal force acting thereon as the propeller rotates. For this purpose, in the left hand end face of the cylinder l8, as shown'in Fig. 1, is formed a circular groove 81 which "abuts on and is sealed by the flange l1 formed integrally with the hub II and sockets H. A hole 88 is drilled through the wall of each socket H to meet the groove 81, and a slot 88 in the inner surface of the socket connects the hole 88 with the space below the lowermost of the thrrust bearings 46, thus providing a free passage from the interior of the socket to the groove 81-. Accordingly, with such an arrangement centrifugal force acting on the lubrbicant in all of the blade sockets during rotati n of the propeller hub will force lubricant from any socket containing a greater amount of lubricant than the others along the slot 88 through the hole 88 into the circular groove 81 and thence, through similar passages, to the socket or sockets containing a lesser amount of lubricant. The flow of lubricant between sockets will thus continue until equalization of level in all sockets is obtained: Obviously, the groove 81 could be replaced by any other type of substantially circular conduit, such as tubing or pipe, adapted to connect the hole" in one socket with similar holes in'the other sockets, or to connect the sockets individually with each other by means of relatively short conduits which may be either straight or curved.

The operation of the above described pitch changing mechanism is as follows:

Through driving connections, which will presently be reviewed, the mechanism as shown in Fig. 1 is so arranged that the pitch of the blades is caused to increase if the piston 28 is moved to the left, providing that the propeller is of the tractor type and that it rotates in a standard clockwise direction when viewed from the engine side thereof. It is apparent that the same effect could be obtained with a pusher type propeller, if the direction of rotation were reversed, or if each rack rod 21 were located on the opposite side of its mating gear 84-a from that shown in Fig. 1. When the piston 28 moves, it carries with it all of the rack rods 21, which are attached to it, and these rods must, therefore, move uniformly and at the same rate. As the rack of gear teeth 88 formed in each rod 21 is'in driving engagement with the corresponding gear segment 84-41 secured to each blade shank 88, it rollows that all of the blades must rotate equally and. at the same rate in response to any movement of the piston 28.

When the-piston 28 is in its extreme righthand position a shown in Fig. 1, the blades are 50 adjusted that their pitch is at the lowest limit required for ordinary service, and when the piston is moved to its extreme left-hand position the blade pitch is increased to the highest limit required for such service, which covers the range uitable for taking off, climbing and cruising at various speeds and altitudes. In the majority of cases, this range necessitates avariation in pitch angle of the blades amounting to about 20 to 30',

and the relative dimensions employed in the accompanying drawings are so chosen as to provide for a variation within such limits. Obviously, however, a greater or smaller variation may readily be obtained, as desired, by increasing or decreasing the stroke of the piston 28, or by decreasing or increasing the pitch diameter of the gear segments 34-a, or by any combination of such alterations.

As is well known in the art, when a propeller is rotating at operative speeds and the blade pitch is within the ordinary range; the action of centrifugal force on the blades is such as, to tend to rotate each blade in its socket towards its low pitch limit, and this tendency, which is usually termed centrifugal twisting moment, attains considerable proportions, even in the case of relatively small propellers, amounting to at least several thousand inch-pounds of torque for a set of blades. In the present invention, the force thus developed is utilized, through the medium of the blade gears 8|-a and rack rods 21; for moving the piston 28, Fig. 1, in a right-hand direction in the cylinder i8, so that .no spring,

hereinbefore described, and it would have the advantage of being adaptable for use with established standard propeller shaft designs, which would require no special machining. or other modification, but the cost of the hub would be increased appreciably.

As another example of an obvious modiflcation, it is apparent that whereas in the above tween the head 2| and the piston 23, Fig. 1, in

order to move the latter to the left. It is apparent that the quantity of oil thus admitted to the cylinder will determine the extent of the longitudinal movement of the piston and, therefore, the degree of increase in the pitch of the blades.

Conversely, it is equally apparent that the blade pitch may be decreased to any extent desired within the normal range by permitting oil in corresponding quantity to drain from the cylinder l8, thus allowing the piston 23 to be moved proportionately to the right by the force exerted thereon through the centrifugal twisting action of the blades.

The flow of oil or other fluid through the tube '66 and transfer ring 59 to and from the hydraulic cylinder l8 may be controlled by any of the wellknown arrangements now in use. Such controls could' be operated either manually or automatically as by a constant speed governor, or a combination of manual and automatic controls could be employed. The essential functions of the control would be to alter the pitch of the propeller blades by permitting fluid, such as oil, to flow through the tube 66 to and from the cylinder I9 in the proper amounts at the desired time. Another function of the control would be to maintain the propeller blades in fixed pitch positions 'by closing the tube 66 or an extension thereof, or by allowing fluid to flow therethrough to the cylinder in proper quantity to compensate for any leakage that may occur in the cylinder itself or in the conduits leading thereto.

From what has preceded, it is obvious that all of the objects enumerated herein are fully and successfully accomplished by the present invention, in the manner and through the means illustrated in the accompanying drawings and described in this specification. It is essential, however, to note that many alterations and modifications of design may readily be made in detail and general construction without in any way departing from the spirit and scope of the invention.

For example, by referring to Fig. 1, it is apparent that the cylinder l8 could be fabricated integral with the hub I. It is also evident that the central barrel of the hub l I, which surrounds thev propeller shaft I2, may be extended to the right in the general form of a tube, with the right-hand end thereof terminating approximately in line with the threaded end of the sleeve portion 51 of the cylinder head 2|. The inside diameter of such an extension of the hub would be slightly greater than the outside diameter of the shaft l2 and its sectional area would prefera'bly beas small as practical limitations would permit.- The bores .of the piston 23 and head 2| would be increased to fit slidably over the outer surface of this tubular extension, which would be made smooth, and dependent dimensions of these and other parts would be adjusted in accordance with such changes. The operation of a modified design of this nature would clearly be precisely the same as that of the arrangement described arrangement, the piston 23 is movable longitudinally and the cylinder 18 is stationary with respect to the hub II, this design could be readily reversed without any change in the principle of operation; that is, the piston could be fixedly secured to the shaft l2 or hub II and the cylinder could be detached from the hub and made slidable'along the shaft. In such a case, the rack rods 21 would be secured by a suitable head or other means to the cylinder instead of to the piston, and each of these rods would also have to be re-located with respect to its mating blade gear, in addition to certain other minor alterations, 1

As a further example of a modification which may under certain circumstances be desirable, a self-centering ringer or washer may be included in the ,oil transfer device to compensate for possible inaccuracies in the alignment of the component parts thereof. Such a washer would be installed between the nut 58 and the ring 59, Fig. l, and'its inside diameter would be slightly greater than the outside diameter of the sleeve portion 51 of the head 2| so as to permit of limited radial adjustment. The left-hand face of the washer would be ground flat to form an oil seal with the mating face of the ring 59 and its right-hand face would be substantially spherical in form, either convexor concave. hand face of the nut 58 would also be spherical in shape and adapted to cooperate with the matin spherical face of the washer so as to substantially centralize the pressure exerted thereon by the nut when tightened, thus causing the oil-seal face of the washer to bear uniformly against the mating face of thering 59, regardless of misalignment between the nut 58 and the sleeve 51. Preferably, the washer would be so mounted .on the sleeve 51 as to be freely movable longitudinally thereof but restrained from rotation relatively thereto, as by means of a, feather key or looselyfitting splines.

Among many additional obvious modifications are the following:

Whereas the fluid transfer ring 59 is shown as having circular ducts or grooves 62 and 61 in its opposite. faces,,it is apparent that the same principle of operation would still obtain if either or both of these grooves were omitted, providing that a corresponding groove or grooves were cut in the face 6| of the head 2| or in the face 58-11 of the nut 58, or in both of the faces GI and 58-11.

Whereas the design of th fluid transfer device above described provides a hydrostatically balanced ring between two adajcent fluid sealing members, it is apparent that in cases where such a balanced condition is not essential, thering need have fluid sealing contact with only one adjacent member, and may have any suitable type of thrust bearing contact with the other adjacent member. For example, the ring 59 may have fluid Sealing contact with the surface 6| of the head 2| and plain sliding contact against the thrust nut 58, in which case the groove Win the ring could be omitted and other means could be readily provided for lubricating the thrust surfaces,

The left- Whereas the nut BI is shown as having threaded engagement with the sleeve 51 of the head 2 I, it is apparent that as the function of this nut is primarily to press the ring 59 against the surface ll, the same result. could be obtained by threading the nut to any other member, as the shaft I! or a separate sleeve attached to the engine housing 8 l Whereas the sleeve 51 of the head 2| is shown as extending through the bore of the ring 58, it

is apparent that the same function could be performed by a similar sleeve connected with the 1 head 2| extending around the outer periphery of placed thereon as are imposed by th prior art or are specifically set forth in the appended claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. An aeronautical propeller adapted to be mounted on a shaft extending from a power plant, comprising a hub secured to the shaft having blades Journalled therein for pitch change, each blade adjacent its butt end and within the hub having a gear thereon; reciprocable rack elements mounted within the hub each engaging one said blade butt gear, said rack elements having integral extensions passing slidably through the wall of said hub toward said power plant; an annular piston loosely fitted around the engine shaft between the hub and power plant and reciprocable therealong, to which the ends of said changing movement to said blades through said racks and gears; a cylinder secured to the face of said hub through which said rack extensions pass, said cylinder being concentric with said shaft and defining therewith an annular chamber in which. said piston is movable, said piston having a loose fit relative to the wall of said cylinder, means to drain the hub end of said cylinder to the power plant, annular cup seal means on the face of said piston remote from the hub, said seal means engaging said shaft and the inner wall of said cylinder; a head secured to the end of said cylinder remote from the hub, said head embracing said shaft, means to seal said head to said shaft; said cylinder, piston and head rotating bodily with said shaft and hub; and relatively rotatable fluid transfer means wholly without the confines of said power plant having a part thereof formed in said head and'an interengaging part thereof secured from rotation, for feeding pressurized fluid to the space bordered by said cylinder, said shaft, said head and said piston.

2. An aeronautical propeller comprising a shaft extending from a power plant, a hub secured to the shaft, said hub having blades journalled therein for pitch change, each blade ad- 12 mounted within the hub each enga in one of said blade butt gears, said rack elements having integral extensions passing slidably through an inboard wall of said hub toward said power plant; an annular piston coaxially arranged around said engine shaft between the hub and power plant and reciprocable axially thereof, and secured to the ends of said rack'extensions, whereby reciprocation of said piston simultaneously imparts pitch changing movement to said blades through said racks and gears; an annular cylinder for said piston, having an end face through which said rack extensionspass and one cylindrical wall rigid with said hub wall, guides in said hub for said rack elements whereby to support said piston from said extensions with a loose fit relative to the wall of said cylinder, said cylinder having a head rotatable with said cylindrical wall at the power plant end of said cylinder, annular seal means on said piston engaging the wall of said cylinder, fiuid connection means while allowing radial movement of said connection means with respect to the power plant, and means providing a rotatable seal between said rotatable head and said keyed fluid connection means.

3. An aeronautical propeller adapted to be mounted on a shaft extending from a power plant, comprising a hub secured to the shaft having blades journalled therein for pitch change, each blade adjacent its butt end and within the hub having a gear thereon; reciprocable rack elements mounted within the hub each engaging one said blade butt gear, said rack elements having integral extensions passing slidably through the wall of said hub toward said power plant; an annular piston loosely fitted around the engine shaft between the hub and power plant and reciprocable therealong, to which the ends of said rack extensions are secured, whereby reciprocation of said piston simultaneously imparts pitch changing movement to said blades through said racks and gears; a cylinder secured to the face of said hub through which said rack extensions pass, said cylinder being concentric with said shaft and defining therewith an annular chamber in which said piston is movable, said piston having a loose fit relative to the wall of said cylinder, means to drain the hub end of said cylinder to the power plant, annular cup seal means on the face of said piston remote from the hub, said seal means engaging said shaft and the inner wall of said cylinder; a head secured to the end of said cylinder remote from hub, said head embracing said shaft, means to seal said head to said shaft; said cylinder, piston and head rotating bodily with said shaft and hub; and relatively rotatable fluid transfer means wholly without the confines of said power plant, said fiuid transfer means comprising a parallel sided annular groove in a portion of said head, said head having an opening establishing communication between the cylinder space and one of the parallel sides of said groove; a parallel sided ring fitted within said groove, means to secure said ring from rotation, and a pressure fluid conduit attached to said ring, the latter having passages formed therein to conduct pressure fluid to both side faces thereof from said conduit, and annuiariy around said 1 8: and mean to adjust the Number clearance of said ring in said groove. 2,174,717- HOWARD MURPHY. 2,144,428 ROBERT E. LINSE. 2,232,683 7 5 2,211,149 REFERENCES CITED 2,135,190 The following references are of record infthe 2,304,153 of this patent 2,123,057 UNITED STATES PATENTS 10 2 173 913 Eumber Name Date Re; 221

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